The present invention relates primarily to a dispenser for gel deodorants or other semisolid products, and particularly to the head of a deodorant dispenser and methods of making the head and otherwise treating porous media so as to have properties desired in a semisolid product dispenser.
Deodorants and antiperspirants (hereinafter jointly referred to as deodorants) are typically applied to the skin of the underarm from some form of dispenser. Years ago aerosol cans were commonly employed to dispense deodorants. Deodorants in solid form have become popular. The solid deodorant is held in a body that has a piston. A cap is removed from the body, and the piston is activated to force the solid deodorant upwardly until the top portion is exposed. The top portion can then be rubbed onto the underarm skin.
Most recently, clear, gel deodorants have been proposed. Other semisolid forms of deodorant, such as creams or soft sticks, have also been suggested. One of the benefits of such semisolid deodorants is that they are less expensive to manufacture, because the fluid nature of the semisolid deodorant allows it to be pumped and easily loaded into a dispenser as part of the manufacturing step. One of the difficulties with dispensing a gel or other semisolid is that there must be a surface onto which the semisolid deodorant is applied, which is then brought into contact with the underarm. One prior art gel deodorant dispenser used a type of a grate. Gel was forced upwardly from within a body holding the gel through holes in the grate. The gel stayed on top of this grate and was then wiped onto the skin of the underarm. The grate was rigid, and was formed by injection molding plastic into a mold. The holes were formed by core pins within the mold.
Another proposal was to take a woven screen material and insert mold the woven screen material into a frame, thus forming a head. However, because the woven screen material was not rigid, it was proposed to include supports within the head to force the screen material to take on a dome shape so that it could contact the skin of the underarm. Several problems have been encountered with this proposal. First, the supports inherently block some of the openings in the screen, and the gel comes out unevenly across the screen. However, if no supports are used, and the screen collapses, all of the gel under the screen will come out, causing an overdose.
Second, the opening size of the screen plays conflicting roles. If the opening size is too large, the gel material will flow out if the dispenser is tipped on its side. On the other hand, if the opening size is too small, the gel material has to be put under such pressure when it is forced through the screen that the gel structure is compromised. For example, the liquid portion of the gel may disassociate from solid portions, or oil and water emulsions of other semisolid deodorants may break. In addition, when a semisolid deodorant is over pressurized, it continues to ooze out even though the user no longer activates the piston, and in fact may have set the dispenser aside after using it. When the user comes back, the deodorant has come through the screen and dried on top of the screen.
Another problem with woven screen material is that it is difficult to provide openings consistently sized any smaller than 400 square microns (20 microns by 20 microns) when making a weave. It is nearly impossible to make an opening smaller than 5 microns by 5 microns using a woven screen. If a media with an opening of 2 microns or less is desired, a porous membrane usually has to be used. Thus, if the semisolid deodorant material has a low viscosity, it may not be possible to make a normal woven screen with a pore size that will prevent the material from leaking out.
Another problem with the use of a woven screen is that the percent open area of a screen gets smaller and smaller as the pore size is reduced. The strands or fibers making the screen must be large enough to give integrity to the screen. As they are placed closer and closer to one another to reduce the pore size, the ratio of open area to area blocked by the fibers is reduced. The problem with a low percentage open area is that the amount of material that can be forced through the screen is reduced as the percent open area is decreased.
Another problem with a woven screen material is that if it is stretched while being manufactured as part of the dispensing head, especially around the edges when a rounded shape piece of media is used, the openings are not uniform. More deodorant could come out of the larger openings than the openings in the middle of the piece of media.
Besides the porous media itself, there are other difficulties in making a head for a semisolid product dispenser. Because the semisolid product is a gel or some other fluid material, all of the passageways between where it is stored and where it is dispensed must be fluid tight so that the product does not leak out under pressure. If parts of the dispenser are made out of an inexpensive thermoplastic material such as polypropylene, it is difficult to form leak-free joints between the parts, as polypropylene does not normally form strong bonds between parts. At times, ultrasonically welded parts only look like they are bonded because polypropylene is soft and the parts deform instead of welding together. Later, when under pressure, the parts come apart. Such a joint would be unacceptable in a semisolid product dispenser, as the dispenser head could come apart when the product was forced through it, causing the gel deodorant or other semisolid product to gush out and make a mess in the hands of the user as the joint came apart. Other thermoplastic materials could be used, but their cost would be a significant disadvantage where the dispenser is made in mass quantities and only used once before being thrown away.